Haven't been able to find my template for this yet, but I believe those are the dimensions I used too. Sounds about right to me, anyway. I think I used the same Evergreen metal siding sheet styrene for the triangular plant-on in the bottom corner.
The styrene I used was 1/16" thick.
I know @EWilliams did the same thing to turn one into a full hero, turned out great. I'm sure he'd be willing to offer some tips and tricks so you could do the same for yours.
You would be correct, sir I don't have anymore sets of the graphics ("ecl" over at TPZ did them for me), so if you still have the ones that came with the kit, that'd be great!